Tensio-active agents are widely used as surfactants in compositions for household and industrial applications in which they may act as detergents, foaming agents, foam stabilisers, wetting agents, emulsifiers and/or emulsion stabilisers.
The oldest type of tensio-active agents are the alkali soaps of fatty acids. They were mainly used as detergents and are still widely used today in spite of their relatively weak tensio-active properties. Much stronger synthetic surfactants have been developed since. The elder generation of widely used synthetic surfactants was mainly formed of alkyl benzene sulfonates (ABS). However, ABS, in particular branched alkyl benzene sulfonates, presented the disadvantage of causing serious water pollution problems due to their poor biodegradability. Accordingly, ABS have been largely replaced by linear alkyl sufonates (LAS) with ten or more carbon atoms in the alkyl chain and which present improved biodegradability compared to ABS surfactants.
In the search for alternative or improved surfactants, monomeric and dimeric sugars such as glucose and sucrose (saccharose) have been used as starting material for the synthesis of non-ionic derivatives with tensio-active properties.
V. Maunier et al. (Carbohydrate Research, 299, 49-57, (1997)) disclosed tensio-active properties of several 6-aminocarbonyl derivatives of methyl α-D-glucopyranoside and D-glucose and compared them with the properties of the urethane methyl 6-O-(N-heptylcarbamoyl)-α-D-gluco-pyranoside.
The synthesis of several sucrose N-n-alkyl urethanes and their tensio-active properties have been disclosed i.a. by H. Bertsch et al. (J. prakt. Chem., 11, 108 (1960)) and by W. Gerhardt (Abh. Dtsch. Akad. Wiss. Berlin, Kl. Chem., Geol. Biol., Vol 1966 (6), 24-32, (1967)). The urethanes are prepared by reacting sucrose with the corresponding n-alkyl isocyanate (H. Bertsch et al. o.c.) and by reacting sucrose with potassium cyanate in the presence of a selected n-alkyl halogenide in dimethyl formamide (W. Gerhardt, o.c.). The derivatives present moderate to good tensio-active properties but only at rather high concentration and the sucrose n-alkyl urethane derivatives with long alkyl chains suffer from poor solubility in water.
To overcome the poor solubility in water of the monomeric and dimeric sugar n-alkyl urethanes, several approaches were examined, including the synthesis of n-alkyl urethanes of ethoxylated or propoxylated monomeric and dimeric sugars and the synthesis of alkoxylated alkyl urethanes of monomeric and dimeric sugars. The synthesis and tensio-active properties of n-alkyl urethanes derived from ethoxylated and propoxylated sucrose, respectively mannitol, have been disclosed by W. Gerhardt (o.c. and German Patent DE 1 518 696). The synthesis and tensio-active properties of 1-(n-alkyloxy)-ethylurethanes of sucrose have been disclosed by T. Lesiak et al. (J. prakt. Chem., 319 (5), 727-731, (1977)).
Moreover, the preparation of miscellaneous urethanes derived from various carbohydrates have been disclosed.
I. Wolff et al. (J. Am. Chem. Soc., 76, 757 (1954)) mentioned to have prepared urethanes of starch, but later studies by E. Asveld et al. (Carbohydrate Polymers, 4, 103-110, (1984)) revealed that in the aqueous reaction conditions used by I. Wolff et al. no urethanes but only mixtures of the carbohydrate and urea compounds were formed.
European patent application EP 0 801 077 discloses n-(C1-C18) alkyl urethanes of cellulose and alkoxylated cellulose. Similarly, German patent application DE 43 38 152 A1 discloses n-alkyl urethanes of starch and partially acetylated starch. Both patent applications disclose the use of the alkyl urethanes as thermoplastic material but are completely silent about possible tensio-active properties of said urethanes.
European patent application EP 0 157 365 discloses various urethane derivatives of polysaccharides including alkyl carbamates of cellulose, amylose, chitosan, dextran, xylan and inulin, and discloses their use for the optical resolution of racemic mixtures. No mention is made of possible tensio-active properties of the carbamates.
In co-pending European patent application EP 98870135.5 (applicant: Tiense Suikerraffinaderij n.v.), tensio-active alkyl urethanes of fructans, particularly of inulin, are described.
In view of the steadily increasing demand for surfactants and the increasing severity of national and supra-national Regulations with respect to toxicity and biodegradability of surfactants for household and industrial use, the search for alternative and for more efficient and/or better biodegradable surfactants is continually going on.